The invention relates to devices for physical, chemical, radiological, or biological detection, and more particularly to radio frequency sensor circuitry based sensing devices for physical, chemical, radiological, or biological detection in the presence of metals.
Radio frequency identification (RFID) tags are widely employed for identification of animals, garments, consumer goods, combinatorial chemistry reaction products, and detection of unauthorized opening of containers. For such applications, the conventional passive RFID tags are preferred due to their low cost (less than $1). For sensing applications that involve detecting change in temperature, and pressure, traditional RFID tags require a specific redesign of portions of their electronic circuitry. Disadvantageously, such RFID sensors also often require a battery.
In free space, the electromagnetic field of the RFID tag is undisturbed. However, if the RFID tag is placed on or in a metallic surface (in proximity to metal), the magnetic flux through the metal substrate induces eddy currents within the metal that opposes the reader's magnetic field. This dampens the magnetic field in the metal to an extent that communication between the reader and transponder may no longer be possible. A similar issue of impaired readability exists with articles or products composed of water or liquid.
RFID systems have been recently applied for wireless sensing applications. For example, RFID-based temperature sensors, bacterial sensor RFID tags are employed in sensing applications. Similar to RFID tags, sensors based on RFID tags are also negatively affected in presence of metals or liquids. Accordingly, operation of passive RFID based sensors is conventionally prohibited in close proximity to metal surfaces (such as walls of metal containers, etc.).
Therefore, it would be desirable to provide a device that would enable a RFID based sensor to operate in metallic and/or liquid environments.